The present invention relates to a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire. More particularly, it relates to a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of two wheel tires of both front wheels or rear wheels.
An apparatus for detecting decrease in tire air-pressure (DWS) in which decompression of a tire is detected on the basis of rotational (wheel speed) information of four wheel tires attached to a vehicle is conventionally known. Such an apparatus employs a theory that a rotational velocity or a rotational angular velocity of a decompressed tire is increased when compared to remaining normal tires owing to a decrease in outer diameter (dynamic load radius of the tire) from that of a tire of normal internal air-pressure. In a method for detecting decrease in internal pressure on the basis of a relative difference in rotational angular velocities of tires (reference should be made to Japanese Unexamined Patent Publication No. 305011/1988),   DEL  =                    {                                            (                              F1                +                F4                            )                        /            2                    -                                    (                              F2                +                F3                            )                        /            2                          }            /              {                              (                          F1              +              F2              +              F3              +              F4                        )                    /          4                }              xc3x97    100    ⁢          (      %      )      
is employed as a judged value DEL. Here, F1 to F4 denote rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
However, since decompression is judged on the basis of a difference in sums of rotational angular velocities of the four wheels which are respectively located diagonally with respect to each other, it is impossible to simultaneously detect decompression of both front wheels or both rear wheels. It therefore exists the danger that fuel consumption is worsened through increase in rolling resistance of the tire and that a burst might be caused upon continuing running without being aware of decompression.
In view of the above facts, it is an object of the present invention to provide a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of both front wheels or both rear wheels.
In accordance with a first aspect of the present invention, there is provided a method for detecting decrease in tire air-pressure, which detects decrease in internal pressure of a tire on the basis of rotational information obtained from tires attached to a vehicle, the method including the steps of: detecting rotational information of the respective tires; storing rotational information of the respective tires; detecting whether the vehicle is running on a flat road or not; detecting whether the vehicle is accelerating or decelerating; comparing rotational information of both front wheels with rotational information of both rear wheels when it has been determined that the vehicle is running on a flat road and that the vehicle is neither accelerating nor decelerating; and judging simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and both rear wheels and a specified threshold.
In accordance with a second aspect of the present invention, there is provided an apparatus for detecting decrease in tire air-pressure, which detects decrease in internal pressure of a tire on the basis of rotational information obtained from tires attached to a vehicle, the apparatus including: rotational information detecting means which detect rotational information of the respective tires; a rotational information storing means which stores the rotational information of the respective tires; a running condition detection means which detects whether the vehicle is running on a flat road or not; an acceleration/deceleration detection means which detects whether the vehicle is accelerating or decelerating; a comparison means which compares rotational information of both front wheels with rotational information of both rear wheels when it has been determined that the vehicle is running on a flat road and that the vehicle is neither accelerating nor decelerating; and a decompression judging means which judges simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and both rear wheels and a specified threshold.
In accordance with a third aspect of the present invention, there is provided a program for judging decompression of a tire, in which for judging decrease in tire air-pressure of a tire, a computer is made to function as a rotational information storing means which stores the rotational information of the respective tires; a running condition detection means which detects whether the vehicle is running on a flat road or not; an acceleration/deceleration detection means which detects whether the vehicle is accelerating or decelerating; a comparison means which compares rotational information of both front wheels with rotational information of both rear wheels when it has been determined that the vehicle is running on a flat road and that the vehicle is neither accelerating nor decelerating; and a decompression judging means which judges simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the rotational information of both front wheels and both rear wheels and a specified threshold.